BY

Robert delMas for their teaching and mentoring, enormous expert knowledge and good conversations. Particularly, I want to thank my adviser Mark Davison for his incredible supports and patience to walk me through this work. I would like to thank Robert Semmes for allowing me to use his data. I would like to thank my colleague, Catherine Close, for her great help at the early stage of this project. I would like to thank my best friend Yu Chen in Finland, who just has finished her degree in Computer Science this summer, for her reminders and encouragements every day. With this “overseas support network ” we built together, I was able to set aside all the distractions, sometimes even frustrations, and to concentrate on writing. I would like to thank my parents, Yuefeng Gong and Jiujia Huang who have been loving and supporting me unconditionally since I was born. I must thank my parents for their effort to help me become an educated, responsible and compassionate person. What is more important, they taught me how to be a happy person. The secret is to listen, to share and to give. Last but not least, I would like to thank Wei Zhang, who has been kind and loving since the first day we met. His love and support without any complaints has enabled me to complete this thesis